Hydraulic test method and hydraulic test device

A water hydraulic test on test pipes having a wide range of sizes is conducted accurately, efficiently, and economically, by using a plurality of booster cylinders arranged in parallel with respect to a test pipe and having respective boosting ratios increasing in stages. A plurality of servo motor driven pumps arranged in parallel is used as a drive source for the plurality of booster cylinders. Before a water pressure on an output side of the booster cylinder reaches a pressure near a test pressure, the plurality of servo motor driven pumps operates simultaneously. Then, the plurality of servo motor driven pumps stops operating except one and the water pressure on the output side of the booster cylinder is increased to the test pressure by the one servo motor driven pump. During pressure increase, the plurality of booster cylinders is used in turn in order of increasing boosting ratio.